Background: Dermal papilla cells (DPCs) play a key role in hair regeneration and morphogenesis. Therefore, tremendous efforts have been made to promote DPC hair inductivity. Objectives: The aim of this study was to investigate the mitogenic and hair inductive effects of hypoxia on DPCs and examine the underlying mechanism of hypoxia-induced stimulation of DPCs. Methods: DPCs' hair inductivity was examined under normoxia (20% O2) and hypoxia (2% O2). Results: Hypoxia significantly increased the proliferation and delayed senescence of DPCs via Akt phosphorylation and downstream pathways. Hypoxia upregulated growth factor secretion of DPCs through the mitogen-activated protein kinase pathway. Hypoxia-preconditioned DPCs induced the telogen-to-anagen transition in C3H mice, and also enhanced hair neogenesis in a hair reconstitution assay. Injected green fluorescent protein-labelled DPCs migrated to the outer root sheath of the hair follicle, and hypoxia-preconditioning increased survival and migration of DPCs in vivo. Conditioned medium obtained from hypoxia increased the hair length of mouse vibrissa follicles via upregulation of alkaline phosphatase, vascular endothelial growth factor, and glial cell line-derived neurotrophic factor. We examined the mechanism of this hypoxia-induced stimulation, and found that reactive oxygen species (ROS) play a key role. For example, inhibition of ROS generation by N-acetylcysteine or diphenyleneiodonium treatment attenuated DPCs' hypoxia-induced stimulation, but treatment with ROS donors induced mitogenic effects and anagen transition. NADPH oxidase 4 is highly expressed in the DPC nuclear region, and NOX4 knockout by CRISPR-Cas9 attenuated the hypoxia-induced stimulation of DPCs. Conclusions: Our results suggest that DPC culture under hypoxia has great advantages over normoxia, and is a novel solution for producing DPCs for cell therapy. Whatʼs already known about this topic?. Dermal papilla cells (DPCs) play a key role in hair regeneration and morphogenesis, but they are difficult to isolate and expand for use in cell therapy. Tremendous efforts have been made to increase proliferation of DPCs and promote their hair formation ability. What does this study add?. Hypoxia (2% O2) culture of DPCs increases proliferation, delays senescence and enhances hair inductivity of DPCs. Reactive oxygen species play a key role in hypoxia-induced stimulation of DPC. What is the translational message?. Preconditioning DPCs under hypoxia improves their hair regenerative potential, and is a novel solution for producing DPCs for cell therapy to treat hair loss.
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